1. Field of the Invention
The present invention relates to apparatus for electroacoustic energy conversion and particularly to a conversion apparatus comprising a channel for an electrical signal to be converted, said channel comprising in series connection signal processing means for processing said electrical signal and having in sequence a power amplifier and an electroacoustic transducer means, such as a loudspeaker.
2. Description of the Prior Art
An example of an apparatus comprising a channel for an electrical signal to be converted and having in sequence a power amplifier and a loudspeaker, is disclosed in U.S. Pat. No. 4,052,560 issued to J. B. Santmann. Energy conversion in this field is apt to suffer from distortion. The fidelity of the acoustical reproduction of an electrical signal representing a recorded sound signal appears to be frequency dependent. Additional approaches to overcome such distortion as to be attributed to signal conversion in acoustic reproduction apparatus are disclosed in U.S. Pat. No. 3,646,270, issued to T. Shiga et al., U.S. Pat. No. 4,071,782, issued to N. Vidovic, and U.S. Pat. No. Re. 29,529 to A. M. Healett. In each of the disclosures signal equalization is directed to signals or signal portions in the audio frequency range only. Signal processing stops at 20 kHz or below in accordance with conventional considerations of high fidelity reproduction.
However, a loudspeaker or electroacoustical energy conversion device generally has a set of preferred vibration modes. Some of these modes are related to fundamental frequencies of vibration, while others are harmonic modes. Harmonic modes are very likely to be in a frequency range above audio. Harmonic modes absorb energy at the expense of the fundamental mode of vibration. These spurious modes operate as energy sinks since they do not contribute to aural sensations.